The use of trocars to obtain access into a body cavity for laparoscopic/endoscopic procedures is well known. These types of procedures are currently in use extensively in such procedures as appendectomies, herniorrhaphies, and gall bladder surgery as large incisions in the cavity wall to obtain access to the body member are not necessary.
A trocar generally comprises a trocar housing, a stylet (i.e., a pointed instrument for penetrating a body cavity wall), and a protective housing or cannula surrounding the stylet. The trocar is used to penetrate the body cavity to provide a passageway into the interior thereof such that instruments used during surgery can be extended through the cavity wall to the surgical site. These instruments can include video probes, cutters, surgical staplers, etc.
As a result thereof, in cutting through the body tissue, muscle and membrane of the body cavity wall, resistance to the cutting edge of the trocar is encountered. However, once the tip of the trocar extends through the cavity wall into the body cavity, the resistance to the cutting force of the trocar is significantly reduced. In accordance therewith, trocars in the past have been designed to attempt to obtain a retraction of the sharp tip immediately upon entry of the sharp tip into the body cavity. Without appropriate means to retract the sharp tip, the sharp point could extend further into the body easily injuring a body member. Since the trocar system employs relatively minor incisions in the cavity wall, if a body member is accidentally punctured, the puncture may not become readily apparent until after the laparoscopic/endoscopic procedure. Such a puncturing of the body member will at the very least impede the patient's recovery from the laparoscopic/endoscopic procedure and could mandate corrective surgery.
In the past, prior trocar systems have attempted to provide for retraction of the sharp tip into a protective tube or cannula once the sharp tip enters the body cavity of the patient. For instance, in U.S. Pat. No. 4,902,280 to Lander, a protective tube is positioned over the sharp tip of the stylet to protect the patient from unwarranted cutting, and additionally, the surgeon from injury due to inadvertent contact with the sharp tip. A concentric protective tube is slidably spring-biased in U.S. Pat. No. 4,902,280 to cover the sharp tip of the trocar. In use, the protective tube moves proximally to expose the sharp tip to allow it to puncture the cavity wall. After the sharp tip of the stylet and the protective tube pass fully into the body cavity, the protective tube is able to slide distally under the force of the spring to once again cover the sharp tip of the stylet to prevent inadvertent tissue injury.
U.S. Pat. No. 4,535,773 to Yoon relates to a trocar system wherein the sharp tip of the stylet, which protrudes from a protective housing for the purpose of puncturing tissue, also carries pressure sensors which signal the reduction of pressure due to the sharp tip passing through the cavity wall into the cavity body. This signal causes a solenoid, located within the protective housing, to become energized and thereby disable a detent which retains the stylet in an extended position, thus allowing a pre-tensioned spring to retract the stylet into the protective housing.
The trocar systems of U.S. Pat. Nos. 4,535,773 and 4,902,980, however, have been found to be disadvantageous in implementation. For instance, U.S. Pat. No. 4,902,980 requires that the protective tube in conjunction with the stylet pass fully through the cavity wall in order to invoke its protective features. Thus, the sharp tip does not retract at the moment of peritoneal penetration thus increasing the chance that the sharp tip will extend further through the body cavity puncturing a body member.
A disadvantage of the trocar system disclosed in U.S. Pat. No. 4,902,980 is that since the protective housing surrounding the sharp tip of the stylet penetrates fully through the cavity wall with the stylet into the body cavity, the protective housing can capture body tissue of the cavity wall therein. Obviously, such retainment of tissue can hinder the withdrawal of the protective tube from the cavity wall as the cavity wall trapped by the tube may lead to further complications.
Even though U.S. Pat. No. 4,535,773 teaches a means of retracting the stylet within the housing when the sharp tip enters the body cavity, the impracticality of providing pressure sensors on the stylet and the unreliability of the solenoid together with the need to provide electrical power along with the associate costs of these additional parts combine to make this approach extremely impractical. Additionally, since the necessary sensing equipment for the trocar system of U.S. Pat. No. 4,535,773 is remote from the trocar housing, the retraction of the stylet is delayed thereby reducing the reliability of the trocar system disclosed therein.